As the number of mobile equipments increases and the need for transferring great amounts of information, such as video and audio signals, over wireless communications systems has increased, the capacity requirements imposed on the mobile communication systems have been substantially restricted. In communication systems based on CDMA-technology and its derivatives, the capacity is mainly limited by multi-user interference occurring between the transceivers using the same carrier frequency, and by fading of the communication channels due to multi-path propagation of a radio signal.
According to prior art solutions, the capacity of a mobile communication system is increased by using sectorization of a cell of a base station. In sectorization, the cell of a base station is physically divided into several sub-cells, which are possibly further separated by sector-specific coding. If the radiation pattern of each sector were ideal, the capacity of the cell would increase linearly as a function of the number of sectors.
The prior art solutions provide very limited tools for increasing the capacity of a mobile communication system. The limitations arise from the fact that the sectors overlap giving rise to multi-user interference, and from the fact that the sectorization cannot fully resolve the problems of the fading channels.